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Improvements to perovskite solar cells (PSCs) have focused on increasing their power conversion efficiency (PCE) and operational stability and maintaining high performance upon scale-up to module sizes. We report that replacing the commonly used mesoporous–titanium dioxide electron transport layer (ETL) with a thin layer of polyacrylic acid–stabilized tin(IV) oxide quantum dots (paa-QD-SnO 2 ) on the compact–titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL–perovskite interface. The use of paa-QD-SnO 2 as electron-selective contact enabled PSCs (0.08 square centimeters) with a PCE of 25.7% (certified 25.4%) and high operational stability and facilitated the scale-up of the PSCs to larger areas. PCEs of 23.3, 21.7, and 20.6% were achieved for PSCs with active areas of 1, 20, and 64 square centimeters, respectively.

We develop a series of polymer donors containing carbazole-based units (CBT) to achieve high-performance (PCE of 15.54%) and thermally stable PSCs.

The epitaxial growth of high-quality thin films provides a powerful method for the rapid preparation of new materials and discovery of materials with promising properties. Here, we report the effect of substrate temperature on the epitaxial growth of high-quality and large-area epitaxial CdTe films on GaAs(100) by molecular beam epitaxy. RHEED patterns as a function of the substrate temperature showed sharp streaky lines. A CdTe epilayer grown at 320 °C showed the narrowest full-width at half-maximum (FWHM) of 180 arcsec from (004) reflection in X-ray rocking curve measurements. The smooth and flat surface observed in the AFM image showed the excellent uniformity of the thin film, and the surface roughness decreased monotonically with the substrate temperature. From the substrate temperature dependence of the (A0, X) emission line, the luminescence intensity was found to increase with increasing substrate temperature, while the FWHM decreased with substrate temperature. Our experimental data suggest that the substrate temperature plays an important role in establishing hetero-epitaxial film growth for semiconductor devices.

The concurrent enhancement of short-circuit current (JSC) and open-circuit voltage (VOC) is a key problem in the preparation of efficient organic solar cells (OSCs). In this paper, we report efficient and stable OSCs based on an asymmetric non-fullerene acceptor (NFA) IPC-BEH-IC2F. The NFA consists of a weak electron-donor core dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (BEH) and two kinds of strong electron-acceptor (A) units [9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) with a tricyclic fused system and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC2F)]. For comparison, the symmetric NFAs IPC-BEH-IPC and IC2F-BEH-IC2F were characterised. The kind of flanking A unit significantly affects the light absorption features and electronic structures of the NFAs. The asymmetric IPC-BEH-IC2F has the highest extinction coefficient among the three NFAs owing to its strong dipole moment and highly crystalline feature. Its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels lie between those of the IPC-BEH-IPC and IC2F-BEH-IC2F molecules. The IPC group also promotes molecular packing through the tricyclic π-conjugated system and achieves increased crystallinity compared to that of the IC2F group. Inverted-type photovoltaic devices based on p-type polymer:NFA blends with PBDB-T and PM6 polymers as p-type polymers were fabricated. Among all these devices, the PBDB-T:IPC-BEH-IC2F blend device displayed the best photovoltaic properties because the IPC unit provides balanced electronic and morphological characteristics. More importantly, the PBDB-T:IPC-BEH-IC2F-based device exhibited the best long-term stability owing to the strongly interacting IPC moiety and the densely packed PBDB-T:IPC-BEH-IC2F film. These results demonstrate that asymmetric structural modifications of NFAs are an effective way for simultaneously improving the photovoltaic performance and stability of OSCs., A 9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) moiety in asymmetric non-fullerene acceptors promotes the formation of a densely packed crystalline structure, enabling efficient and long-term stable organic solar cells.

Nonfused-ring electron acceptors (NFREAs) have received increasing attention for use in organic solar cells (OSCs) because of their synthetic simplicity and tunable optical spectra. However, their fundamental molecular interactions and the mechanism by which they govern the property-function relations of OSCs remain elusive. Here, to investigate the effects of the structural symmetry of NFREAs, two acceptor-donor-acceptor'-donor-acceptor (A-D-A'-D-A)-type NFREAs, 2,2'-(((naphtho[1,2

In early studies on organic solar cells with high conductivity PEDOT:PSS, the contact between ITO and PEDOT:PSS was considered ohmic. However, because low-conductivity PEDOT:PSS (such as AI4083) is mainly utilized in contemporary solar cells, the contact between ITO and PEDOT:PSS is not ohmic anymore. Despite the high possibility that there are serious interface problems, little attention has been paid to the interface between PEDOT:PSS and ITO. Most of the previous studies of interfaces in organic solar cells have focused on the interface between the active and charge transport layers. In this work, we have employed a conjugated polyelectrolyte that uses potassium poly[9,9-bis(3′-sulfonatopropyl)fluorene-alt-(9-(2,7-diethylheptyl)-carboazole)] (WPFSCz-) between ITO and low-conductivity PEDOT:PSS to overcome complicated organic–inorganic interfacial problems. The insertion of the WPFSCz- layer provides substantial advantages in the operation of polymer solar cells. First, the inserted WPFSCz- layer modifies the work-function of ITO, thereby forming an effective cascading energy alignment, which is favorable for good hole transport. Second, the introduction of the WPFSCz- layer eliminates interfacial trap sites. The reduction in traps reduces recombination losses at the interface, resulting in an improvement in the fill factor. These effects result in a significant increase in the efficiency of non-fullerene solar cells based on PM6 and Y6, from 15.86 to 17.34%. In addition, we have found that the problem of the interface in contact with ITO occurs not only in PEDOT:PSS, but also in oxide-based charge transport layers. We have confirmed that the insertion of the WPFSCz- layer between ITO and an MoO3 (or ZnO) charge transport layer shows the same positive results.

In addition to the phase-separated morphology of donor and acceptor, the internal field created by work-function difference between cathode and anode can also influence the exciton dissociation probability. In this study, we have demonstrated enhanced photovoltaic performance by increasing exciton dissociation efficiency. To improve both work-function modification effect and charge transport properties, we have incorporated novel carbon quantum dots (CQD) having NH2 ligands into the polyethyleneimine (PEI) work-function modifying layer as a dopant. A study of net photocurrent density as a function of effective voltage showed that devices with a CQD-doped PEI layer had a much higher charge separation probability compared to devices with a pristine PEI layer. A Kelvin-probe force microscopy study demonstrated that a CQD-doped PEI layer induced lower work-function of ITO than that of ITO with a pristine PEI, which induced a stronger internal field. This strengthened internal field induced better exciton dissociation efficiency, thereby improving solar cell performance.

While hole extraction is crucial for the external quantum efficiency of conventional n-i-p colloidal quantum dot (CQD) solar cells (CQDSCs), sulfur-passivated p-type CQDs (pCQDs) have been the best...

The fullerene acceptor, which has historically been used in bulk-heterojunction (BHJ) organic solar cells, is being replaced by non-fullerene acceptors due to its problem of high energy loss (Eloss). To reduce the energy loss in BHJ organic solar cells as a means to improve open-circuit voltage (Voc), several approaches have been applied to diminish recombination loss, notably enhancements to film morphology and decreasing of trap states by improving the crystallinity of active components. However, the adjustment of trap density by means of morphology control only has an inevitable limit. In this work, we have investigated the use of a ternary configuration as an alternative way to mitigate the energy loss in fullerene-based BHJ solar cells. A ternary system based on the wide-band-gap polymer PBDTTPD-HT, the small molecule DRCN5T, and PC71BM showed cascading charge transfer from PBDTTPD-HT through DRCN5T to PC71BM, an indirect electron transfer that avoided the deep charge transfer state between PBDTTPD-HT and PC71BM. DRCN5T:PC71BM mixture has a high ECT level close to the singlet state energy of DRCN5T, leading to low energy loss between DRCN5T and PC71BM and thereby greatly reducing the probability of first-order recombination. Consequently, the incorporation of a small amount of DRCN5T as a secondary donor into the PBDTTPD-HT:PC71BM system enhanced overall PCE, an effect mostly attributed to enhancement of Voc by means of eliminating charge transfer energy losses.

Ambipolar organic field-effect transistors (A-OFETs) allow a significant reduction in the complexity of organic integrated circuits (ICs) because they act as both n- and p-type transistors. In this paper, we report an efficient A-OFET based on the bilayer architecture of p-type poly(benzodithiophene(2-thienyl)-pyrrolopyrrole-dione) (PBDTTPPD) and n-type [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). By achieving the saturation condition of the dichloromethane (DCM) solvent for preparing the PCBM solution, we successfully obtained a complete bilayer of PCBM and PBDTTPPD and used it as a carrier transport layer in an A-OFET. The A-OFET exhibits clear bipolar transport and operates as an n-type and a p-type transistor in a single device. When a positive bias is applied between the gate electrode and the source electrode, the A-OFET serves as an n-type transistor with an n-channel generated for electron transport at the interface of PCBM and PBDTTPPD. On the other hand, it serves as a p-type transistor with a p-channel generated for hole transport at the interface between PBDTTPPD and SiO2 when a negative bias is applied. The bipolar transport is modulated by morphology control using a 1,8-diiodooctane (DIO) additive and the PBDTTPPD layer thickness. The optimized A-OFET shows reasonable carrier mobilities for an ambipolar transistor with an average electron mobility of 2.22 × 10−3 cm2 V−1 s−1 and an average hole mobility of 2.29 × 10−3 cm2 V−1 s−1. An efficient ambipolar organic transistor (A-OFET) based on the bilayer architecture of p-type poly(benzodithiophene(2-thienyl)-pyrrolopyrrole-dione) (PBDTTPPD) and n-type [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was demonstrated. The A-OFET exhibits clear bipolar transport and operates as an n-type and a p-type transistor in a single device.

Doping is a widely-implemented strategy for enhancing the inherent electrical properties of metal oxide charge transport layers in photovoltaic devices because higher conductivity of electron transport layer (ETL) can increment the photocurrent by reducing the series resistance. To improve the conductivity of ETL, in this study we doped the ZnO layer with aluminum (Al), then investigated the influence of AZO on the performance of inverted bulk heterojunction (BHJ) polymer solar cells based on poly [[4,8-bis [(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b’]dithiophene-2,6-diyl]-[3-fluoro-2[(2-ethylhexyl)-carbonyl]-thieno-[3,4-b]thiophenediyl ]] (PTB7):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The measured conductivity of AZO was ~10−3 S/cm, which was two orders of magnitude higher than that of intrinsic ZnO (~10−5 S/cm). By decreasing the series resistance (Rs) in a device with an AZO layer, the short circuit current (Jsc) increased significantly from 15.663 mA/cm2 to 17.040 mA/cm2. As a result, the device with AZO exhibited an enhanced power conversion efficiency (PCE) of 8.984%.

Polypyrrole nanoparticles (PPy-NPs) with excellent near-infrared absorption are commonly used as photothermal therapy (PTT) agents; however, PTT using PPy-NPs has a limitation in that it is difficult to maximize their therapeutic effect because of the lack of specific targeting. In this study, to overcome the difficulty of targeting, folic acid functionalized carbon dots (FA-CDs) with bright green fluorescence properties were combined with carboxylated PPy-NPs via the EDC/NHS coupling reaction to yield a PTT imaging agent. The synthesized FA-CD/PPy-NPs with excellent photostability performed folate receptor (FR) positive HeLa cancer cell imaging by green fluorescence signals of FA-CDs and exhibited high cell viability (above 90%) even at 500 μg/mL. The viability of HeLa cells incubated with 200 μg/mL FA-CD/PPy-NPs was dramatically decreased to 25.02 ± 1.85% by NIR laser irradiation, through photothermal therapeutic effects of FA-CD/PPy-NPs with high photothermal conversion efficiency (η = 40.80 ± 1.54%). The cancer cell death by FA-CD/PPy-NPs was confirmed by fluorescence imaging of FA-CDs as well as live/dead cell staining assay (calcein-AM/PI). These results demonstrate that the FA-CD/PPy-NPs can be utilized as multifunctional theranostic agents for specific bioimaging and treatment of FR-positive cancer cells.

Two new Y6 derivatives of symmetrical YBO-2O and asymmetrical YBO-FO nonfullerene acceptors (NFAs) are prepared with a simplified synthetic procedure by incorporating octyl and fluorine substituents onto the terminal 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN) moiety. By moving the alkyl substituents on the Y6 core to the terminal INCN moiety, the lowest unoccupied molecular orbital of the YBO NFAs increases without decreasing solubility, resulting in high open-circuit voltages of the devices. Molecular dynamics simulation shows that YBO-2O/-FO preferentially form core-core and terminal-terminal dimeric interactions, demonstrating their tighter packing structure and higher electron mobility than Y6, which is consistent with 2D grazing incidence X-ray scattering and space charge limited current measurements. In blend films, the hole transfer (HT) from YBO-2O/-FO to the polymer donor PM6 is studied in detail by transient absorption spectroscopy, demonstrating efficient HT from YBO-FO to PM6 with their suitable energy level alignment. Despite the simplified synthesis, YBO-FO demonstrates photovoltaic performance similar to that of Y6, exhibiting a power conversion efficiency of 15.01%. Overall, this design strategy not only simplifies the synthetic procedures but also adjusts the electrical properties by modifying the intermolecular packing and energy level alignment, suggesting a novel simplified molecular design of Y6 derivatives.

We investigate the photovoltaic characteristics of organic solar cells (OSCs) for two distinctly different nanostructures, by comparing the charge carrier dynamics for bilayer- and bulk-heterojunction OSCs. Most interestingly, both architectures exhibit fairly similar power conversion efficiencies (PCEs), reflecting a comparable critical domain size for charge generation and charge recombination. Although this is, at first hand, surprising, a detailed analysis points out the similarity between these two concepts. A bulk-heterojunction architecture arranges the charge generating domains in a 3D ensemble across the whole bulk, while bilayer architectures arrange the specific domains on top of each other, rather than sharp bilayers. Specifically, for the polymer PBDB-T-2F, we find that the enhanced charge generation in a bulk composite is partially compensated by reduced recombination in the bilayer architecture, when nonfullerene acceptors (NFAs) are used instead of a fullerene acceptor. Overall, we demonstrate that bilayer-heterojunction OSCs with NFAs can reach competitive PCEs compared to the corresponding bulk-heterojunction OSCs because of reduced nonradiative open-circuit voltage losses, and suppressed trap-assisted recombination, as a result of a vertically separated donor-to-acceptor nanostructure. In contrast, the bilayer-heterojunction OSCs with the fullerene acceptor exhibited poor photovoltaic characteristics compared to the corresponding bulk devices because of highly aggregated acceptor molecules on top of the polymer donor. Although free carrier generation is reduced in a in a bilayer-heterojunction, because of reduced donor/acceptor interfaces and a limited exciton diffusion length, more favorable transport pathways for unipolar charge collection can partially compensate the aforementioned disadvantages. We propose that the unique properties of NFAs may open a technical venue for the bilayer-heterojunction as a great and easy alternative to the bulk heterojunction.

Tin oxide (SnO2) is widely adopted as an electron transport layer in perovskite solar cells (PeSCs) because it has high electron mobility, excellent charge selective behavior owing to a large band gap of 3.76 eV, and low-temperature processibility. To achieve highly efficient SnO2-based PeSCs, it is necessary to control the oxygen vacancies in the SnO2 layer, since the electrical and optical properties vary depending on the oxidation state of Sn. This study demonstrates that the performance of PeSCs may be improved by using nitrogen-doped graphene oxide (NGO) as an oxidizing agent for SnO2. Since NGO changes the oxidation state of the Sn in SnO2 from Sn2+ to Sn4+, the oxygen vacancies in SnO2 can be reduced using NGO. Multiple devices are fabricated, and various techniques are used to assess their performance, including X-ray photoelectron spectroscopy, dark current analysis, and the dependence of the open-circuit voltage on light intensity. Compared with the average power conversion efficiency (PCE) of control devices, PeSCs with SnO2:NGO composite layers exhibit greater PCEs with less deviation. Therefore, the introduction of NGO in a SnO2 layer can be regarded as an effective method of controlling the oxidation state of SnO2 to improve the performance of PeSCs.

Novel donor-donor type alternating copolymers (8CDT-TT and 16CDT-TT) derived from cyclopentadithiophene (CDT) and thienothiophene (TT) moieties that differ from solubilizing side chains were successfully synthesized and characterized. After the synthesis of CDT-TT-based conjugated polymers with dioctyl and dihexadecyl side chains, their optical, thermal, structural and semiconducting properties were investigated. Organic thin-film transistors fabricated from 8CDT-TT and 16CDT-TT exhibit carrier mobilities as high as 3.92×10-4 and 1.05×10-3 cm2V-1s-1, respectively. Bulk heterojunction solar cells fabricated using a polymer:PCBM blend ratio of 1:3 exhibit power conversion efficiencies of 2.12 and 1.84% for 8CDT-TT and 16CDT-TT, respectively.

In this study, we present efficient semi-transparent solar cells with enhanced performance at low intensity illumination via the incorporation of emissive quantum clusters consisting of 22 Au atoms. The inclusion of Au22 quantum clusters (Au22-QCs) in semi-transparent solar cells led to a substantial reduction of the dependence on the incident light intensity as well as an increase in device efficiency. For the control semi-transparent solar cell, which has ~ 25% transparency, there was a 35% drop in efficiency with a light intensity decrease of 40% (0.6 sun). However, for the semi-transparent solar cell with Au22-QCs, there was only a 15% drop in efficiency under 0.6 sun irradiation. Less dependence on incident light intensity can be a great advantage in the practical use of semi-transparent solar cells. The change in the intensity of the incident light can also be caused by simply changing the angle of the light and device. Thus, the performance of general solar cells is strongly dependent on the angle of incident light. However, such angle dependence was effectively suppressed in solar cells with Au22-QCs. Furthermore, less dependence on the angle of incidence light offered a great advantage in driving flexible solar cells. The performance difference between the flat state and bending state was significantly reduced in our semi-transparent flexible solar cell with Au22-QCs.

We investigated the effect of three different additives (1-chloronaphthalene, 1,8-diiodooctane, diphenylether) on the performance of polymer-polymer solar cells based on a BHJ blend consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) as a donor and poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) as an acceptor. A direct comparison of the efficiency of the solar cells with and without additive indicated that the device using the additive exhibited slightly improved performance. However, the efficiency enhancement was not significant. The optimal ratio of additive differed depending on the properties of the additive. In addition, the performances of polymer-polymer solar cells were not significantly dependent on the type of additive. Identifying the optimal fabrication condition was critical for achieving the highest performance. It is known that the general role of an additive in polymer solar cells based on a BHJ active layer was to induce good phase separation between the donor and acceptor by morphology modification. However, grazing-incidence wide-angle X-ray scattering results showed that no significant morphology change in polymer-polymer active layer was caused by the additive. Rather, our modulated impedance spectroscopy study showed that the performance enhancement in polymer-polymer solar cells with additive was because of improved recombination properties rather than improvements in crystalline morphology.

Despite the great potential of carbazole and rhodanine moieties, donor molecule containing carbazole and rhodanine have received less attention because of their limited processability and poor efficiency. In this work, we synthesized a new donor molecule based on a combination of carbazole as a core-unit and rhodanine as an electron-withdrawing end-unit. We introduced diketopyrrolopyrrole as an additional acceptor at a position of π-linker to increase molecular planarity and the overall molecular weight. Our new donor molecule (named LGC-D073) showed a promising PCE value of 6.6% using chlorobenzene as a solvent. Moreover, LGC-D073 exhibited similar performances for both inverted and conventional structures. These results suggest that designing donor molecules with the combination of carbazole and rhodanine can be an efficient new approach to obtain high performance organic solar cells with improved processability.

The beneficial use of a hole transport layer (HTL) as a substitution for poly(3,4-ethlyenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is regarded as one of the most important approaches for improving the stability and efficiency of inverted perovskite solar cells. Here, we demonstrate highly efficient and stable inverted perovskite solar cells by applying a GO-doped PEDOT:PSS (PEDOT:GO) film as an HTL. The high performance of this solar cell stems from the excellent optical and electrical properties of the PEDOT:GO film, including a higher electrical conductivity, a higher work function related to the reduced contact barrier between the perovskite layer and the PEDOT:GO layer, enhanced crystallinity of the perovskite crystal, and suppressed leakage current. Moreover, the device with the PEDOT:GO layer showed excellent long-term stability in ambient air conditions. Thus, the enhancement in the efficiency and the excellent stability of inverted perovskite solar cells are promising for the eventual commercialization of perovskite optoelectronic devices.

Organic–inorganic lead halide perovskites have drawbacks in applications due to insufficient and inadequate understanding of the materials. In particular, it is a priority to investigate CH3NH3PbI3 due to its suitable properties and its band gap energy of about 1.59 eV. In this work, we investigated the perovskite crystal with respect to structural, electronic, and optical properties because a single crystal is an ideal platform for examining essential characteristics. The spatial distribution of the perovskite structure was identified by transmission electron microscopy and Kelvin probe force microscopy. The built electronic structure is an important index for the carrier types depending on the surface potential distribution. In particular, a potential variation showed a mixture of the perovskite phase and a decomposed phase on the surface, which also implied the role of surface imperfections as initiation sites for degradation. Therefore, it is critical to verify the carrier types on the surface to enhance the possibilities of improvements for applications.

Nickel oxide (NiO) offers intrinsic p-type behavior and high thermal and chemical stability, making it promising as a hole transport layer (HTL) material in inverted organic solar cells. However, its use in this application has been rare because of a wettability problem caused by use of water as base solvent and high-temperature annealing requirements. In the present work, an annealing-free solution-processable method for NiO deposition is developed and applied in both conventional and inverted non-fullerene polymer solar cells. To overcome the wettability problem, the typical DI water solvent is replaced with a mixed solvent of DI water and isopropyl alcohol with a small amount of 2-butanol additive. This allows a NiO nanoparticle suspension (s-NiO) to be deposited on a hydrophobic active layer surface. An inverted non-fullerene solar cell based on a blend of p-type polymer PTB7-Th and non-fullerene acceptor IEICO-4F exhibits the high efficiency of 11.23% with an s-NiO HTL, comparable to the efficiency of an inverted solar cell with a MoOx HTL deposited by thermal evaporation. Conventionally structured devices including this s-NiO layer show efficiency comparable to that of a conventional device with a PEDOT:PSS HTL.

Semi-transparent plastic solar cells are currently highly attractive for their potential as the most prominent components for building-integrated photovoltaics. However, the power conversion efficiency (PCE) of semi-transparent plastic solar cells still lags behind due to the lack of a suitable transparent top electrode which can be easily fabricated. Here, we demonstrate high performance semi-transparent plastic solar cells by introducing an oxide-metal-oxide (OMO) multilayer composed of MoO3 and Ag as a transparent top electrode. Because the conductivity of the OMO electrode is governed by an intermediate Ag layer sandwiched between 2 MoO3 layers, the PCE also strongly depends on the thickness of the intermediate Ag layer in the OMO electrode. By controlling the thickness of Ag layer, we obtained various PCE values from 4.5% with ~50% maximum transparency in the visible region to 9.1% with ~5% maximum transparency in the visible region. In addition, in order to get closer to practical application, 2 sizes of mini-module devices were fabricated on a larger (10.0 cm × 10.0 cm) substrate for outdoor operation and small-sized (7.0 cm × 5.0 cm) substrates for indoor operation were demonstrated using 3 materials of different color.

Hybrid lead halide perovskite possesses attractive properties and outstanding performance. The electronic structure of hybrid lead halide perovskite single crystal can be used to comprehend its intrinsic properties. In this study, the crystal structure of CH3NH3PbBr3 perovskite crystal was elucidated by transmission electron microscopy. Phonon modes and CH3NH3+ rocking modes were analyzed. Band gaps of the crystal were obtained by temperature-dependent Raman scattering spectroscopy and photoluminescence measurement. Surface potential measurement for a (001) plane exhibited a work function of the material and other phases of PbBr2 and CH3NH3Br. From experimentally determined values, an electronic structure of CH3NH3PbBr3 was built. It showed a p-type characteristic.

Wide band gap pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD)-based alternating polymer, P(BDTT-ttPPD) was synthesized by combining electron-rich 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDTT) and electron-deficient 4,6-bis(2-bromothieno[3,2-b]thiophen-5-yl)-5-octyl-2-(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,3(2H, 5H)-dione (ttPPD). When the P(BDTT-ttPPD) polymer was applied to binary polymer solar cells (PSCs) as a donor material, the device exhibited a maximum power conversion efficiency (PCE) of 6.93% with an open-circuit voltage (Voc) of 0.87 V, a short-circuit current (Jsc) of 11.38 mA/cm2, and a fill factor (FF) of 70%. The photovoltaic performance was further improved to 9.08% (Voc ∼ 0.80 V, Jsc ∼ 16.05 mA/cm2, and FF ∼ 71%) when the polymer was used as a donor component for absorbing high-energy light in ternary PSCs with a blend of P(BDTT-ttPPD):PTB7-Th:PC70BM. The overall PCE of ternary PSCs was found to be higher than those of the binary PSCs made form P(BDTT-ttPPD) or PTB7-Th. We discuss the property modulation of PPD-based polymers via the replacement of thiophene π–spacer units with thieno[3,2-b]thiophene.

Two new tercopolymers (RP1 and RP2) containing electron-donating benzodithiophene, weak electron-accepting pyrrolo[3,4-c]pyrrole-1,3-dione derivative and strong electron-accepting 5,6-difluorobenzothiadiazole derivative were prepared. The opto-electrical studies showed that RP1 and RP2 displayed identical optical band gaps (E g ~ 1.72 eV) and highest occupied/lowest unoccupied molecular orbital energy levels (HOMO/LUMO ~ −5.32 eV/−3.60 eV). The polymer solar cells prepared with the configuration of ITO/PEDOT:PSS/RP1:PC70BM (1:1.5 wt%) + 3 vol% DIO/Al and ITO/PEDOT:PSS/RP2:PC70BM (1:1.5 wt%) + 3 vol% DIO/Al exhibited a maximum power conversion efficiency (PCE) of 5.16% (V oc ~ 0.76 V, J sc ~ 10.93 mA/cm2, and FF ~ 0.62) and a PCE of 3.56% (V oc ~ 0.67 V, J sc ~ 9.67 mA/cm2, and FF ~ 0.55), respectively.